The long term goal of this project is to determine the structure and physiological significance of pineal peptides which affect reproduction. The major focus of the proposed project is to determine the distribution and mechanism of action of a novel antigonadotropic decapeptide (AGD) discovered during the last granting period. Acute i.v. injection of either the natural or synthetic AGD reduced serum levels of LH and PRL in rodents. In other experiments pulsatile LH secretion was inhibited by its microinfusion into the third ventricle. Preliminary results suggest that the AGD stimulates the release of dopamine from rat hypothalamic median eminence in vitro, providing a potential site and mechanism for its antigonadotropic action. Polyclonal antisera were raised against the AGD in rabbits and the antibodies purified by affinity chromatography. Also, the AGD was iodinated with (125)I and a radioimmunoassay (RIA) developed for its measurement. Proposed experiments will examine the distribution of endogenous AGD in rat tissues and body fluids by RIA. Immunoreactive AGD will be localized in the central nervous system by immunohistochemistry. Additionally, the distribution of radiolabeled AGD will be examined by autoradiography after i.v. injection. Other experiments will attempt to localize the site of action by acute stereotaxic microinjection of the AGD into a variety of selected sites in the central nervous system. Studies aimed at a determination of the mechanism of action will include an examination of the effects of AGD on catecholamine turnover rates in the preoptic area, hypothalamus and brain stem. The mechanism of the stimulatory effect of the AGD on dopamine release will be also be studied on rat median eminence perifused in vitro. Other experiments will examine its effects on pubertal development and ovulation. Finally, studies will continue on the purification, isolation and structure determination of a bovine pineal GnRH-like peptide.